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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Super-resolution Imaging of Plasmonic Near-Fields: Overcoming Emitter Mislocalizations

Plasmonic nano-objects have shown great potential in enhancing applications like biological/chemical sensing, light harvesting and energy transfer, and optical/quantum computing. Therefore, an extensive effort has been vested in optimizing plasmonic systems and exploiting their field enhancement properties. Super-resolution imaging with quantum dots (QDs) is a promising method to probe plasmonic near-fields but is hindered by the distortion of the QD radiation pattern. Here, we investigate the interaction between QDs and “L-shaped” gold nanoantennas and demonstrate both theoretically and experimentally that this strong interaction can induce polarization-dependent modifications to the apparent QD emission intensity, polarization, and localization. Based on FDTD simulations and polarization-modulated single-molecule microscopy, we show that the displacement of the emitter’s localization is due to the position-dependent interference between the emitter and the induced dipole, and can be up to 100 nm. Our results help pave a pathway for higher precision plasmonic near-field mapping and its underlying applications.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

PbS/CdS Quantum Dot Room-Temperature Single-Emitter Spectroscopy Reaches the Telecom O and S Bands via an Engineered Stability

We synthesized PbS/CdS core/shell quantum dots (QDs) to have functional single-emitter properties for room-temperature, solid-state operation in the telecom O and S bands. Two shell-growth methods–cation exchange and successive ionic layer adsorption and reaction (SILAR)–were employed to prepare QD heterostructures with shells of 2–16 monolayers. PbS/CdS QDs were sufficiently bright and stable to resolve photoluminescence (PL) spectra representing both bands from single nanocrystals using standard detection methods, and for a QD emitting in the O-band a second-order correlation function showed strong photon antibunching, important steps toward demonstrating the utility of lead chalcogenide QDs as single-photon emitters (SPEs). Irrespective of type, few telecom-SPEs exist that are capable of such room-temperature operation. Access to single-QD spectra enabled a direct assessment of spectral line width, which was ~70–90 meV compared to much broader ensemble spectra (~300 meV). We show inhomogeneous broadening results from dispersity in PbS core sizes that increases dramatically with extended cation exchange. Quantum yields (QYs) are negatively impacted at thick shells (>6 monolayers) and, especially, by SILAR-growth conditions. Time-resolved PL measurements revealed that, with SILAR, initially single-exponential PL-decays transition to biexponential, with opening of nonradiative carrier-recombination channels. Radiative decay times are, overall, longer for core/shell QDs compared to PbS cores, which we demonstrate can be partially attributed to some core/shell sizes occupying a quasi-type II electron–hole localization regime. Finally, we demonstrate that shell engineering and the use of lower laser-excitation powers can afford significantly suppressed blinking and photobleaching. However, dependence on shell thickness comes at a cost of less-than-optimal brightness, with implications for both materials and experimental design

36 MATERIALS SCIENCE↗
DOE OSTI2023

Deterministic Localization of Strain-Induced Single-Photon Emitters in Multilayer GaSe

The nanoscale strain has emerged as a powerful tool for controlling single-photon emitters (SPEs) in atomically thin transition metal dichalcogenides (TMDCs). However, quantum emitters in monolayer TMDCs are typically unstable in ambient conditions. Multilayer TMDCs could be a solution, but they suffer from low quantum efficiency, resulting in low brightness of the SPEs. Here, we report the deterministic spatial localization of strain-induced SPEs in multilayer GaSe by nanopillar arrays. The strain-controlled quantum confinement effect introduces well-isolated sub-bandgap photoluminescence and corresponding suppression of the broad band edge photoluminescence. Clear photon-antibunching behavior is observed from the quantum dot-like GaSe sub-bandgap exciton emission at 3.5 K. The strain-dependent confinement potential and the brightness are found to be strongly correlated, suggesting a promising route for tuning and controlling SPEs. The comprehensive investigations of strain-engineered GaSe SPEs provide a solid foundation for the development of 2D devices for quantum photonic technologies.

2D materials↗
DOE OSTI2025

Efficient on-chip terahertz generation and detection with GaN photoconductive emitters

Photoconductive emitters for terahertz generation hold promise for highly efficient down-conversion of optical photons because it is not constrained by the Manley-Rowe relation. Existing terahertz photoconductive devices, however, faces limits in efficiency due to the semiconductor properties of commonly used GaAs materials. Here, we demonstrate that large bandgap semiconductor GaN, characterized by its high breakdown electric field, facilitates the highly efficient generation of terahertz waves in a coplanar stripline waveguide. Towards this goal, we investigated the excitonic contribution to the electro-optic response of GaN under static electric field both through experiments and first-principles calculations, revealing a robust excitonic Stark shift. Using this electro-optic effect, we developed a novel ultraviolet pump-probe spectroscopy for in-situ characterization of the terahertz electric field strength generated by the GaN photoconductive emitter. Our findings show that terahertz power scales quadratically with optical excitation power and applied electric field over a broad parameter range. We achieved an optical-to-terahertz conversion efficiency approaching 100% within the 0.03–1 THz bandwidth at the highest bias field (116 kV/cm) in our experiment. Further optimization of GaN-based terahertz generation devices could achieve even greater optical-to-terahertz conversion efficiencies.

Uzundal, Can B↗
DOE OSTI2024

Tunable quantum emitters on large-scale foundry silicon photonics

Abstract Controlling large-scale many-body quantum systems at the level of single photons and single atomic systems is a central goal in quantum information science and technology. Intensive research and development has propelled foundry-based silicon-on-insulator photonic integrated circuits to a leading platform for large-scale optical control with individual mode programmability. However, integrating atomic quantum systems with single-emitter tunability remains an open challenge. Here, we overcome this barrier through the hybrid integration of multiple InAs/InP microchiplets containing high-brightness infrared semiconductor quantum dot single photon emitters into advanced silicon-on-insulator photonic integrated circuits fabricated in a 300 mm foundry process. With this platform, we achieve single-photon emission via resonance fluorescence and scalable emission wavelength tunability. The combined control of photonic and quantum systems opens the door to programmable quantum information processors manufactured in leading semiconductor foundries.

Larocque, Hugo (ORCID:000900095849780X)↗
DOE OSTI2023

Interplay of molecular dynamics and radiative decay of a TADF emitter in a glass-forming liquid

Herein we investigate the role of molecular dynamics in the luminescent properties of a prototypical thermally activated delayed fluorescence (TADF) emitter, NAI-DMAC, in solution using a combination of temperature dependent time-resolved photoluminescence and absorption spectroscopies. We use a glass forming liquid, 2-methylfuran, to introduce an abrupt change in the temperature dependent diffusion dynamics of the solvent and examine the influence this has on the emission intensity of NAI-DMAC molecules. Comparison of experiment with first principles molecular dynamics simulations reveals that the emission intensity of NAI-DMAC molecules follows the temperature-dependent self-diffusion dynamics of the solvent. A marked reduction of emission intensity is observed as the temperature decreases toward the glass transition because the rate at which NAI-DMAC molecules can access emissive molecular conformations is greatly reduced. Below the glass transition, the diffusion dynamics of the solvent changes more slowly with temperature, which causes the emission intensity to decrease more slowly as well. The combination of experiment and computation suggests a pathway by which TADF emitters may transiently access a distribution of conformational states and avoid the need for an average conformation that strikes a balance between lower singlet–triplet energy splittings versus higher emission probabilities.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Modulation of recombination zone position for white perovskite/organic emitter hybrid light-emitting devices

We report metal halide perovskites present specific challenges as emitters in large area, surface emission lighting devices. Among these challenges is the vast difference in carrier mobilities between the perovskite and many organic buffer layers typically used in such device fabrication as transport and blocking layers. This can make it difficult to engineer recombination to achieve white emitting devices generally. However, in this work, we introduce unique modulation of excitonic confinement within the perovskite layer of the device stack to control overall placement of the recombination zone. This results in a white light emitter that is bright and highly tunable, providing a path to realize white perovskite related light-emitting devices.

42 ENGINEERING↗
DOE OSTI2024

Space Charge Forces analytical model for emittance compensation

Space charge forces represent main induced effects in an RF-injector that degrade the beam quality. In this scenario the laser distribution sent on the photocathode acquires an important role in the emittance compensation process, as the slice analysis shows. Starting from the preliminary studies performed on [1], a novel semi-analytical model of space charge forces is proposed in detail for bunch with arbitrary charge distribution to derive expressions of self-induced forces. The performance of the fields at low energy regime (as the field has not expired RF forces) is under present analysis, we can investigate use of this model in low charge regime. Further, the model has been bench-marked with the behavior of the distributions present in the literature and studied for new ones. It has also been applied for the study of the optimization of a C-band hybrid photoinjector now being commissioned, thus explaining the factor two reduction of the emittance observed at the exit of the gun by changing the initial distribution at the cathode.

Carillo, M.↗
DOE OSTI2022

Single quantum emitters with spin ground states based on Cl bound excitons in ZnSe

Defects in wide-band-gap semiconductors are promising qubit candidates for quantum communication and computation. Epitaxially grown II-VI semiconductors are particularly promising host materials due to their direct band gap and potential for isotopic purification to a spin-zero nuclear background. Here, we show an alternative type of single photon emitter with potential electron spin qubits based on Cl impurities in ZnSe. We utilize a quantum well to increase the binding energies of donor emission and confirm single photon emission with short radiative lifetimes of 192 ps. Furthermore, we verify that the ground state of the Cl donor complex contains a single electron by observing two-electron-satellite emission, leaving the electron in higher orbital states. We also characterize the Zeeman splitting of the exciton transition by performing polarization-resolved magnetic spectroscopy on single emitters. Our results suggest single Cl impurities are suitable as a single photon source with a potential photonic interface.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2023

Interplay between disorder, local relaxation, and collective behavior for an ensemble of emitters outside versus inside a cavity

The interplay between collective optical response and molecular static and dynamic disorder is studied using simple effective Hamiltonians for an ensemble of two-level emitters inside and outside a single-mode cavity. We model environmental disorder by randomly modulating the molecular transition frequencies and the coupling between the emitters and the electromagnetic field. We also consider the effects of intermolecular interactions and orientational disorder. We investigate how these effects lead to new features in the steady-state absorption (outside the cavity), transmission spectra (inside the cavity), and the yield of local molecular processes such as a unimolecular reaction. Outside the cavity, the collective behavior is manifested in the linewidth of the steady-state absorption, the emission spectrum, and the local chemical yield. Inside the cavity, however, the collective behavior primarily determines the Rabi splitting. The effects of intermolecular interactions under orientational disorder are also studied. For the most part, for all types of disorder, if we increase disorder, we find a reduction in the collective nature of the molecular response (smaller effective N) and therefore the Rabi splitting contraction occurs with orientational disorder. Furthermore, we find that static disorder is more destructive to collective behavior than dynamic disorder.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2024

Compensating slice emittance growth in high brightness photoinjectors using sacrificial charge

Achieving maximum electron beam brightness in photoinjectors requires detailed control of the 3D bunch shape and precise tuning of the beam focusing. Even in state-of-the-art designs, slice emittance growth due to nonlinear space charge forces and partial nonlaminarity often remains non-negligible. In this work, we introduce a new means to linearize the transverse slice phase space: a sacrificial portion of the bunch’s own charge distribution, formed into a wavebroken shock front by highly nonlinear space charge forces within the gun, whose downstream purpose is to dynamically linearize the desired bunch core. We show that linearization of an appropriately prepared bunch can be achieved via strongly nonlaminar focusing of the sacrificial shock front, while the inner core focuses laminarly. This leads to a natural spatial separation of the two distributions: a dense core surrounded by a diffuse halo of sacrificial charge that can be collimated. Multiobjective genetic algorithm optimizations of the ultracompact x-ray free electron laser injector employ this concept, and we interpret it with an analytic model that agrees well with the simulations. In simulation, we demonstrate a final bunch charge of 100 pC, peak current ∼ 30 A, and a sacrificial charge of 150 pC (250 pC total emitted from cathode) with normalized emittance growth of < 20 nm rad due to space charge. This implies a maximum achievable brightness approximately an order of magnitude greater than existing free electron laser injector designs. Published by the American Physical Society 2024

43 PARTICLE ACCELERATORS↗
DOE OSTI2025

Impact of Newly Measured 𝛽-Delayed Neutron Emitters around 78 Ni on Light Element Nucleosynthesis in the Neutrino Wind Following a Neutron Star Merger

Neutron emission probabilities and half-lives of 37 𝛽-delayed neutron emitters from 75 Ni to 92 Br were measured at the RIKEN Nishina Center in Japan, including 11 one-neutron and 13 two-neutron emission probabilities and six half-lives for the first time that supersede theoretical estimates. These nuclei lie in the path of the weak 𝑟 process occurring in neutrino-driven winds from the accretion disk formed after the merger of two neutron stars synthesizing elements in the 𝐴∼80 abundance peak. The presence of such elements dominates the accompanying kilonova emission over the first few days and have been identified in the AT2017gfo event, associated to the gravitational wave detection GW170817. Abundance calculations based on over 17,000 simulated trajectories describing the evolution of matter properties in the merger outflows show that the new data lead to an increase of 50%–70% in the abundance of Y, Zr, Nb, and Mo. This enhancement is large compared to the scatter of relative abundances observed in old very metal poor stars and thus is significant in the comparison with other possible astrophysical processes contributing to the light-element production. These results underline the importance of including experimental decay data for very neutron-rich 𝛽 -delayed neutron emitters into 𝑟 -process models.

59 ≤ A ≤ 89↗
DOE OSTI2023

Design of an Emittance Compensation Superconducting Magnet Package for LCLS-II-HE's SRF Photo-Injector

An SRF photo-injector (low frequency, quarter-wave resonator plus emittance compensation magnet) is planned for LCLS-II-HE as it can provide a higher cathode gradient and better electron beam quality than other types of CW electron guns. The magnet package is located immediately downstream of the SRF cavity, and incorporates a solenoid doublet, bucking coils for reduction of the fringe field, normal/skew quadrupoles and horizontal/vertical dipoles. All the magnets are wound of NbTi wire and operate in liquid helium environment. The solenoid package is located inside the SRF gun cryomodule. Design considerations include space limitations, optimal emittance compensation, the magnetic field limits in the superconducting wire and quench protection. The solenoid coils must provide a peak excitation > 25 kgauss 2 ·cm, a fringe field < 20 gauss at the wall of the SRF cavity, an integrated dipole field < 90 gauss·cm and an integrated quadrupole field < 10 gauss. As a result, a genetic algorithm was used to optimize the solenoid design. Correction dipoles and quadrupoles were designed using coil dominated Walstrom style coils.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Hong–Ou–Mandel sensing via superradiant coupling of discrete fluorescent emitters

The Hong–Ou–Mandel (HOM) effect is a fascinating quantum phenomenon that defies classical explanation. Traditionally, remote nonlinear sources have been used to achieve coincident photons at the HOM beam splitter. Here, we suggest that the coincident emission source required for HOM interference can be created locally using superradiant near field coupled emitters positioned across the beam splitter gap. We show that sensitivity to permittivity changes in the beam splitter gap, and corresponding Fisher information can be substantially enhanced with HOM photon detection. Subsequently, we outline several strategies for integration of superradiant emitters with practical sensor systems. Taken together, these findings should pave a way for a wide array of near field HOM quantum sensors and novel quantum devices.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2025

Enhanced spectral purity of WSe 2 quantum emitters via conformal organic adlayers

Quantum emitters in solid-state materials are typically embedded in the bulk of their hosts, making their electronic transitions inaccessible to surface modification. In contrast, two-dimensional materials, with their all-surface nature, offer a platform for tuning quantum emitters via chemical functionalization. Because of its semiconducting properties that enable electrical addressability, monolayer WSe 2 is a promising candidate for quantum emission, although the complex interplay between point defects and the localized strain needed to activate quantum emission leads to poor spectral purity. Here, we demonstrate that functionalizing monolayer WSe 2 with conformal adlayers of 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) improves quantum emission spectral purity. Optical spectroscopy reveals that PTCDA functionalization lowers defect activation energies by 10 meV and induces a 30 nm redshift in quantum emission wavelength, while preserving the bright and dark exciton energies of monolayer WSe 2 . First-principles calculations corroborate these findings, thus providing molecular-level insight into the underlying mechanism of enhanced spectral purity.

Ananth, Riddhi [Northwestern Univ., Evanston, IL (↗
DOE OSTI2021

Transverse Beam Emittance Measurement by Undulator Radiation Power Noise

Generally, turn-to-turn power fluctuations of incoherent spontaneous synchrotron radiation in a storage ring depend on the 6D phase-space distribution of the electron bunch. In some cases, if only one parameter of the distribution is unknown, this parameter can be determined from the measured magnitude of these power fluctuations. In this contribution, we report the results of our experiment at the Integrable Optics Test Accelerator (IOTA) storage ring, where we carried out an absolute measurement (no free parameters or calibration) of a small vertical emittance (5–15 nm rms) of a flat beam by this new method, under conditions, when the small vertical emittance is unresolvable by a conventional synchrotron light beam size monitor.

43 PARTICLE ACCELERATORS↗
DOE OSTI2022

Toward Emittance Measurements at 11.7 GHz Short-Pulse High-Gradient RF Gun

A short pulse high gradient RF gun has been recently tested at Argonne Wakefield Accelerator (AWA) facility. The carried-out test showed that the 1,5-cell gun was able to inject 3 MeV, up to 100 pC bunches at room tem-perature being fed by 9 ns up to 300 MW 11.7 GHz puls-es. The cathode field was as high as about 400 MV/m. So high field is aimed to mitigate repealing Coulomb forces substantially. In accordance with simulations the emit-tance could be as low as less than 0.2 mcm. To obtain so low emittance in the experiment, the gun is assumed to be equipped with a downstream linac to be fed from the same power extractor as the gun itself. Here we report design of the RF power distribution system splitting RF power among the gun and the linac, results of low-power tests, and emittance measurement plans for upcoming new experiment at AWA.

43 PARTICLE ACCELERATORS↗
DOE OSTI2022

EMITTANCE GROWTH DUE TO RF PHASE NOISE IN CRAB CAVITIES

The Electron-Ion Collider (EIC) incorporates beam crabbing to recover geometric luminosity loss from the nonzero crossing angle at the interaction point (IP). It is well-known that crab cavity imperfections can cause growth of colliding beam emittances, thus degrading collider performance. Here we report a particle tracking study to quantify these effects. Presently the study is focused on crab cavity RF phase noise. Simulations were carried out using Bmad. Dependence of emittance growth on phase noise level was obtained which could be used for developing crab cavity phase control specifications. We also benchmarked these simulations with theory.

Huang, H.↗